1. Optimization adjustment of coal grinding system
1.1 Coal mill system process
After the raw coal is dried and grinded by the ball mill, the system exhaust fan is pneumatically transported to the MD dynamic classifier for sorting. The coarse-grained coal powder is pulverized by the screw conveyor to continue grinding, and the finished coal powder is collected by the bag filter. The finished screw conveyor is transported into the pulverized coal bin for use. The process flow is shown in Figure 1.
1.2 Optimization of conveying equipment
Our company's coal mill design production capacity is 25t / h, and the actual mill output is higher, generally around 30 ~ 32t / h. In the case of high production, the coal mill exhaust fan has a large exhaust volume, and the coal powder is more pulverized and the particles are larger. Due to the influence of the particle size and moisture of the powder and the finished product, the configuration of the finished product and the powdered screw conveyor can not meet the high production demand, resulting in serious coal accumulation in the screw conveyor during the actual production process, and the pulverized coal conveying process is blocked, eventually causing the screw conveyor. The motor is tripped or even burned due to current overcurrent, causing equipment failure, which becomes a major failure point of the main equipment that restricts the stable and high-yield operation of the pulverized coal preparation system, which seriously affects the continuous and stable operation of the rotary kiln.
In response to the above situation and in combination with the field equipment layout, the company decided to transform the finished product and the powder back screw conveyor into a FU chain conveyor. Increase the conveying capacity of auxiliary equipment and adaptability to material particle changes, and reduce the chain speed, so that the coal powder entering the FU chain conveyor forms a layer of a certain thickness, preventing and reducing the chain and the track, and between the coal powder And the chance that a friction between the chain and the chain creates static electricity and causes a safety accident. Before and after the optimization adjustment, the main parameters of the powder returning and finished conveying equipment are shown in Table 1.
1.3 Dynamic classifier lubrication optimization
The MD850A coal mill dynamic classifier is designed to use a dry oil pump for manual oil filling to complete the lubrication of the classifier bearings. In actual production, due to the high coal mill output, the loader is heavily loaded during operation, and the dry oil lubrication method makes the bearings have higher temperature due to lack of full lubrication. At the same time, the fineness of the pulverized coal is fine (80μm sieve residue ≤3%), and it is easier to seal into the bearing through the bearing of the classifier. The bearing set temperature is 70°C alarm, and the 80°C classifier jumps. In actual operation, the powder separator bearings are often kept between 75~80°C, which seriously affects the safe and stable operation of the classifier.
It is well known that the dry oil lubrication method has poor fluidity during use, large internal friction resistance, high working pressure, and cannot form a dynamic pressure oil film. At the same time, it is difficult for the grease to spread quickly and effectively to the entire lubrication surface, and it is easy to have a dead angle. The thin oil lubrication method requires low working pressure (generally below 2 MPa), the cost is relatively low, and its flow and heat dissipation performance is good. It can provide all-round lubrication and cooling to the entire working surface or point that needs lubrication, and no lubrication blind zone. . Therefore, we have changed the original dry oil to a thin oil lubrication method. Install a thin oil station next to the MD dynamic classifier, and change the original bearing lubrication point to a thin oil supply; install an oil seal on the upper and lower bearings of the classifier, and install all the oil separators and bearing seals in and out of the classifier. The oil seal is subjected to effective anti-wear treatment to prevent the bearing from being worn out due to leakage of oil through the pipeline, resulting in poor lubrication; the oil return needs to be recycled into the oil tank of the thin oil station through the oil return pipeline for recycling.
1.4 Optimized coal mill operation
After a series of optimization and improvement of the coal grinding system, the coal grinding operation is safe and stable. The powder returning and finished FU chain conveyor meets the production needs of the coal grinding system, and there is no blockage of material transportation caused by high coal grinding or heavy pulverized coal. At the same time, through the optimization of the lubrication method of the coal mill separator, the lubrication effect is better, and the maximum temperature of the bearing during operation is maintained at about 55 °C.
2, kiln tail hot air pipeline optimization adjustment
2.1 kiln tail hot air pipe process layout
The kiln tail of our company is equipped with a waste heat power generation system. The temperature of the exhaust gas discharged from C1 is about 320 °C. After the waste heat is used, the exhaust gas temperature is about 200 °C. In normal production, the kiln exhaust gas enters the humidification tower through the waste heat power generation and high temperature fan to settle, and then provides hot air for the raw material vertical grinding system or directly discharges to the atmosphere through the kiln tail. Since the temperature of the inlet gas of the humidification tower is not high after the waste heat power generation is put into operation, the humidification tower is generally not put into operation, but the exhaust gas also needs to be transported to the top of the humidification tower, and the work of the kiln tail fan is increased. The layout of the high-temperature fan outlet pipe before the optimization is shown in Figure 2.
2.2 Determination of the optimization plan
Combined with the actual situation on site, the high-temperature fan outlet and the bottom of the humidification tower are directly connected by non-standard pipelines, thereby reducing the gas running resistance. When the raw material mill is running, the high-temperature fan exhaust gas is not settled by the humidification tower, and the non-standard pipeline directly optimized and transformed into the vertical mill system; when the raw material is ground into the milled air temperature, it can pass through the non-standard pipeline. The butterfly valve opening degree is controlled to achieve the adjustment of the inlet wind temperature and the inlet air temperature of the kiln tail bag dust collector; when the raw material mill stops grinding, the high temperature fan exhaust gas still passes the original process pipe, that is, enters the humidification tower Settling and cooling at the top. The layout of the high-temperature fan outlet pipe after optimization and transformation is shown in Figure 3.
2.3 Kiln tail fan and vertical mill operation after pipeline optimization
From the actual operation of the optimized kiln exhaust fan and high temperature fan, the use of non-standard pipe is conducive to energy saving and consumption reduction of the entire kiln exhaust system, and at the same time has little interference with the operation of the high temperature fan. When the raw material vertical mill is put into operation, the hot gas removed by the high temperature fan at the kiln tail is not settled by the humidification tower but directly passed through the bottom of the humidification tower through the non-standard process pipeline, and the airflow running distance is shortened and the resistance is reduced. The kiln tail fan works less.
By optimizing the operating parameters, the kiln exhaust fan speed is reduced from 880r/min before optimization to 780r/min, while the outlet pressure of high temperature fan can be maintained in the range of -800～-1 000Pa, which has no adverse effect on the rotary kiln thermal system. .
From the operation of the raw material vertical mill, since the dust-containing gas of the high-temperature fan is not settled in the humidification tower, but directly brought into the raw material vertical mill by the airflow, the raw material grinding powder has a certain ability to be selected, to a certain extent. The production capacity of the raw mill was reduced, and the production at the time of the plant was reduced from 235 t/h before optimization to 231 t/h.
In terms of economic efficiency, the fan speed can be reduced by 192.51 kW per hour, but the raw material grinding power consumption increases from 22.06 kWh/t to 22.39 kWh/t. Therefore, the raw material grinding power consumption per hour increases by 76.23 kW. According to the annual average operating rate of 65%, the comprehensive electricity price is 0.5 yuan/kWh, and the annual direct cost savings is about 330,000 yuan.
3 Conclusion
For different systems and different working conditions, the feasibility analysis of field equipment and process layout optimization should be strengthened, the target and expected effect should be determined, and then rationally optimized and transformed to reduce the power consumption, energy consumption, and production cost of the process. The purpose of the economic benefits of the enterprise.
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